Safety mechanism for saws

ABSTRACT

An improvement is set forth in a sawing apparatus having a workpiece support structure and an operator moveable electrically operated saw having a first normally biased off switch controlling application of electric power thereto, the switch being positioned to be controlled by the hand of an operator which controls movement of the saw. The improvement comprises a device adapted for gripping, positioning and clamping a workpiece relative to the workpiece support structure and a second normally biased off switch connected in series with the first normally biased off switch, the second switch being positioned to be controlled by the off hand of the operator while the off hand is utilizing the device. Since both hands of an operator must be holding onto normally off switches and since both switches are in positions removed from the area of movement of the saw blade, the operator is protected from accidently cutting himself. Yet, the device allows the operator adequate control of the workpiece being cut and further allows the radial arm saw to function as a ripping saw without interference.

TECHNICAL FIELD

This invention relates to an improvement in a sawing apparatus such as apowered rotary milter saw or a radial arm saw. More particularly theinvention relates to an improved safety feature to prevent the user ofsuch an apparatus from accidently injuring his off-hand (hand notpresently encumbered or necessary to actuate the sawing apparatus) orthe fingers of the off-hand by moving them into the area of the sawblade when the saw blade is moving.

BACKGROUND ART

A number of devices are known for clamping workpieces which are fed intoa machine.

U.S. Pat. No. 3,073,589, issued Jan. 15, 1963 to G. Hohwart discloses awork clamping fixture which is commonly used to hold a workpiece duringa machining operation. The workpiece is clamped between a stationary anda movable jaw. The movable jaw is carried by and reciprocially actuatedto and from the clamping position by slidably mounted posts through arack and pinion which also acts to operate double cone locks when thework is clamped to hold the work securely by friction.

U.S. Pat. No. 2,667,903, issued Feb. 2, 1954 to R. A. McCallum describesa sawing machine with a sequentially operated holder-guard and saw. TheMcCallum saw is used primarily to cut mine timbers to the proper size.The saw guard also serves as a work holder, and a single fluid actuatedmotor performs the sequential operations of moving the saw guard intoposition to hold timber, and then advancing the saw against the timberfor the cut. A reverse set of sequential operations takes place afterthe cut is completed.

U.S. Pat. No. 3,939,746, issued Feb. 24, 1976 to G. W. Rogers, et al.discloses a saw guard for a circular saw having a workpiece holder thatmoves relative to the saw blade. The saw guard is mounted on the leadingedge of the workpiece holder, and is moved into a shielding positionadjacent the cutting edge of the blade while the work piece holder isbeing restocked.

U.S. Pat. No. 4,206,672, issued June 10, 1980 to W. A. Smith describesyet another type of work holder in combination with a saw guard. Thecombination guard and work holder comprise two parallel plates pivotallyattached to a jig and operable to swing downward on opposite sides of athrough-slot to clamp the workpiece and to enclose the saw blade as theworkpiece is advanced into the blade.

U.S. Pat. No. 1,600,604, issued Sept. 21, 1926 to A. Sorlien discloses aboard holder for sawing machines. The board holder is attachable to thesaw guide and is adjustable towards or away from the saw so that it maybe disposed over any desired part of the board. A serrated eccentricmounted in a sleeve holds the board in place and prevents the board frombeing kicked back out by the rotating saw blade.

None of the aforementioned patents actively prevents the user of a sawfrom advancing his off-hand in the vicinity of the blade when the bladeis operating. Therefore, numerous accidents occur wherein the operatorof such a blade structure loses one or more of his fingers or otherparts of his off-hand due to just such an accident.

DISCLOSURE OF THE INVENTION

The present invention is directed to overcoming one or more of theproblems as set forth above.

In accordance with an embodiment of the present invention, animprovement is set forth in a sawing apparatus having a workpiecesupport structure and an operator moveable electrically powered sawhaving a first normally biased off switch controlling application ofelectrical power thereto, the switch being positioned to be controlledby the hand of an operator which controls movement of the saw. Theimprovement is in the nature of a device adapted for gripping,positioning and clamping a workpiece relative to the workpiece supportstructure. The improvement further includes a second normally biased offswitch connected in series with the first normally biased off switch.The second switch is positioned to be controlled by the off hand of theoperator while the off hand is utilizing the workpiece gripping,positioning and clamping device.

An apparatus in accordance with the present invention positivelyprevents the operator of a sawing apparatus from moving his off handfingers or other parts of his off hand into the cutting area of theblade since the operators hands must both be occupied to actuate andoperate the sawing apparatus, one guiding the saw while the other graspsthe device for gripping, positioning and clamping the workpiece. This isnecessary since each switch must be separately engaged or the blade willcease to rotate. The device is very preferably operated in connectionwith an automatic brake which positively and swiftly brakes the sawblade on interruption of power to the motor which motivates the sawblade. A conventional blade guard can also be utilized in combinationwith the improvement of the present invention. Furthermore, for suchmachinery as a radial arm saw where the saw blade can be arranged alongthe length of the workpiece support structure and the workpiece can beripped, an override switch can be provided which is engaged only byrotation of the saw blade into the riping position.

BRIEF DESCRIPTION OF DRAWINGS

The invention will be better understood by reference to the figures ofthe drawings wherein like numbers denote like parts throughout andwherein:

FIG. 1 illustrates, in front left perspective, an improved sawingapparatus in accordance with an embodiment of the present invention asmounted to a conventional powered miter saw (in phantom);

FIG. 2 illustrates, in a similar view to FIG. 1 but on a much largerscale and in more detail, the embodiment of the present invention shownin FIG. 1;

FIG. 3 illustrates, schematically, the electric power circuit foroperation of the embodiment of FIG. 1, and in phantom, an optionalfeature useful with radial arm saws;

FIG. 4 illustrates, in side view, the embodiment of FIG. 1 positionedready to clamp a workpiece;

FIG. 5 illustrates, in a view similar to FIG. 4, how a workpiece isgrasped by the embodiment of FIG. 1;

FIGS. 6 and 7 are partial views in enlarged scale showing successivegrasping of a workpiece by the embodiment of FIG. 1;

FIG. 8 illustrates a workpiece grasped by the embodiment of FIG. 1 andbeing moved along the workpiece support and relative to the position ofa saw blade; and

FIG. 9 illustrates, in rear partial view, a detail in the structure ofthe embodiment of FIG. 1.

BEST MODE FOR CARRYING OUT THE INVENTION

An improved sawing apparatus 10 in accordance with the present inventionincludes (FIGS. 1, 2 and 3) a workpiece support structure 12 and anoperator moveable electrically powered saw blade 14 having a firstnormally biased off switch 16 which controls application of electricalpower from an electrical power source 18 to a motor 20 which rotates thesaw blade 14. The switch 16 is positioned to be controlled by the handof an operator which controls movement of the saw 14. A conventionaltransparent plastic saw guard 22 may be provided to deter objects orbody parts from being placed in the cutting area of the blade 14.Movement of the blade 14 is controlled by the operator grasping a handgrip 24 and pulling downwardly to move the blade 14 downwardly throughthe position of a workpiece 26. In miter saw arrangements the angle ofthe blade 14 relative to the workpiece 26 can be adjusted since thesupport 28 for the saw 14 will generally be slidably and pivotallymounted to the support structure 12. Note that the operator must bedepressing the switch 16 or the blade will not be powered by the motor20.

It is preferred that conventional means 30 (FIG. 3) be provided forautomatically braking the blade 14 when the powering circuit for themotor 20 is broken. This can be accomplished, for example, by use of asolenoid 32 which normally serves to overcome the force of a spring 34sufficiently to prevent a brake 36 from contacting the motor 20. Whenpower is interrupted in the circuit to the motor 20, the solenoid 32 isno longer activated whereby the spring 34 pulls downwardly upon theillustrated lever 38 which, acting via the fulcrum 40 leads toapplication of the brake 36 to the motor 20.

In accordance with the present invention, a device 42 (FIG. 1) isprovided which is adapted for gripping, positioning and clampingworkpiece 26 relative to the workpiece support structure 12. The device42 is best seen in overall view in FIG. 2 and is useful with the supportstructure 12, seen in FIG. 1. Generally, the device 42 fits on top of atable 44, or forms part thereof, which forms a part of the supportstructure 12. A fence 46 is generally attached to the table 44 andserves for guiding the workpiece 26. The fence 46 generally has anopening 47 whereat the saw 14 can be moved to cut the workpiece 26. Aframe 48 forms a part of the device 42 and is located adjacent the fence46. The frame 48 has a base 50 which is parallel generally to the table44 or a part thereof and which extends away from the fence 46. Aclamping construction 52 is provided which is adapted to pressdownwardly upon the workpiece 26 and to grip the workpiece 26 betweenitself and the base 50. Frame positioning means 54 are provided forpositioning the frame 48 laterally across the table 44 generallyparallel to the fence 46 when the workpiece 26 is gripped by the device42. In the embodiment illustrated the frame positioning means 54includes a slide structure 56 along the fence 46 and parallel to thetable 44. A slide mating structure 58 extends along the frame 48parallel to the table 44, the slide mating structure 58 mating with theslide structure 56 in sliding fit therein. This allows reciprocalmovement of the frame 48 along the fence 46 and parallel to the table44. A lever 60 having a hand grip portion 62 is pivotally mountedrelative to the fence 46 and table 44 at a pivot 64. The lever 60 ismounted (see FIG. 8) whereby, so long as the lever 60 is not movedsufficiently to immovably clamp the workpiece 26 in a single position,if it is moved sideways relative to the fence 46 it impels the frame 48sideways via its pivotal attachment to a bar 66 at a pin 67. Thus, thelever 60 is adapted to exert a force upon the frame 48, which force isgenerally parallel to the slide structure 56.

The lever 60 is also further adapted to move the clamping construction52 downwardly upon the workpiece 26 to grip and eventually clamp theworkpiece 26 in a single position. Adverting to FIGS. 4 and 5, the lever60 can be pivoted downwardly rotating the bar 66. In such a situation,the pivot 64 moves along a circular track 68. A pair of cranks 70, 72(FIG. 2) are rigidly mounted to the rod 66 and are moved clockwise inFIGS. 4 and 5 whereby they exert downward forces via links 74 and 78(see FIG. 2) thereby pushing downwardly upon clamps 80 and 82.

The bottoms of the clamps 80 and 82 grip the workpiece 26 by frictionand are selected to have a higher coefficient of friction than does thebase 50. Accordingly, so long as the clamps 80 and 82 do not bear downupon the workpiece 26 sufficiently so as to immobilize it, latera1movement of the lever 60 leads to lateral movement of the workpiece 26.

FIGS. 6 and 7 illustrate another feature of the preferred clampingconstruction 52. In particular, the preferred clamping construction 52includes means 88 for urging the workpiece 26 laterally towards thefence 46. The particular means 88 illustrated is in the nature of a pairof interlocking sawtooth members 90 and 92, both a part of the clamps 80and 82 which, when the clamps 80 and 82 are clamped downwardly upon theworkpiece 26 lead the lowermost 92 of the members 90 and 92 to be forcedleftwardly in FIGS. 6 and 7 towards the fence 46. By friction theworkpiece 26 is similarly moved. At the same time, the workpiece isimmobilized to prevent lateral and other movement thereof.

In accordance with the present invention it is required that a switch 94(FIG. 2) which is normally biased off, be connected in series with thefirst normally biased off switch 16, all as shown in FIG. 3. The secondswitch 94 must be positioned to be controlled by the off hand of theoperator, which off hand is utilizing the device 42. In the particularembodiment illustrated the switch 94 is shown as being mounted to thelever 60 at the hand gripping portion 62 thereof. Thus, a user must bemaking use of the lever 62 and depressing the switch 94 at the same timehe is gripping the saw grip 24 and depressing switch 16, or the saw willnot rotate.

FIG. 3 also illustrates an embodiment of the invention, in phantom,wherein a third normally biased off switch 96 is connected in parallelacross the first and second switches 16 and 94. This embodiment of thepresent invention is useful wherein the saw 14 is in the nature of aradial arm saw which is used for ripping workpieces 26. In such aninstance, the third normally biased off switch 96 may be placed in theon position selectively by positioning the radial arm saw in positionfor ripping the workpiece 26.

Note that in the embodiments illustrated the fence 46 is ofsubstantially one piece construction. A fence 46 such is as used in andwith the apparatus 10 of the present invention can replace aconventional fence normally supplied with a radial arm saw or miter sawor the like. Alternatively, a device in accordance with the presentinvention can be mounted to an existing fence, or part of an existingfence can be removed and a replacement partial fence adapted tocooperate with the improved apparatus of the present invention can beinstalled in its place.

INDUSTRIAL APPLICABILITY

The improved sawing apparatus 10 in accordance with the presentinvention is useful with miter saws or rotary arm saws. Its purpose isto prevent an inattentive operator of such an apparatus, or one who isattentive and is bumped or slips while operating the apparatus, fromplacing his fingers or other portions of his anatomy in jeopardy duringoperation of the overall sawing apparatus 10.

While the invention has been described in connection with certainspecific embodiments thereof, it is to be understood that suchdescription was for convenience only and that other objects andadvantages of the invention will become apparent to one skilled in theart from the foregoing description and the accompanying drawings and theinvention includes such advantages and objectives and includes suchmodifications as may be apparent to one of skill in the art to which theinvention pertains, all of which fall within the scope of the inventionas defined by the appended claims.

We claim:
 1. In a sawing apparatus having a workpiece work supportstructure and an operator moveable electrically powered saw blade havinga first normally biased off switch controlling application of electricpower thereto, said switch being positioned to be controlled by a handof an operator which controls movement of the saw blade, an improvementcomprising:a device adapted for gripping, positioning and clamping aworkpiece relative to said workpiece work support structure; and asecond normally biased off switch connected in series with said firstnormally biased off switch, said second switch being positioned to becontrolled by the off hand of the operator while the off hand isutilizing said device.
 2. An improved sawing apparatus as set forth inclaim 1, further including:a third normally biased off switch connectedin parallel across said first and second switches, said third switchbeing selectively positionable in its on position.
 3. An improved sawingapparatus as set forth in claim 1, wherein said support structureincludes a table and a fence for guiding said workpiece and wherein saiddevice includes:a frame adjacent said fence, said frame having a baseparallel to said table and extending away from said fence and a clampingconstruction adapted to press downwardly on said workpiece and tosandwich said workpiece between itself and said base; and frame movingmeans for moving said frame laterally across said table generallyparallel to said fence.
 4. An improved sawing apparatus as set forth inclaim 3, wherein said frame moving means includes a slide structurealong said fence parallel to said table, a slide mating structure alongsaid frame parallel to said table, and a lever pivotally mountedrelative to said fence and adapted to exert a force upon said framegenerally parallel to said slide structure.
 5. An improved sawingapparatus as set forth in claim 4, wherein said lever is further adaptedto move said clamping construction downwardly upon said workpiece.
 6. Animproved sawing apparatus as set forth in claim 5, wherein said secondswitch is carried by said lever in position for operator activation. 7.An improved sawing apparatus as set forth in claim 3, wherein saidclamping construction further includes means for urging said workpiecelaterally towards said fence.
 8. An improved sawing apparatus as setforth in claim 1, further including:means for braking the saw blade inresponse to interruption of said electric power.